RU2740510C1 - Method for determination of optimum period of oil well injection wells for low-permeability reservoirs - Google Patents

Abstract

FIELD: oil, gas and coke-chemical industries.

SUBSTANCE: invention relates to a method for determination of optimal period of development for injection wells for low-permeability reservoirs. Method comprises selecting flooding elements representing drilled or projecting and production wells, for which injection wells are to be planned for injection, wherein the injection wells are reactive and according to them dynamics of yields is tracked, and remaining wells are perturbing, perform predictive calculations for two scenarios, when all wells reacting and disturbing, are launched into production, and when reacting wells are launched into production, and disturbing wells are left inactive, wherein reaction of injection well to input of production well is determined, for which for each injection well there is calculated normalized oil flow rate in each scenario per each time step of the forecast period, reaction of operation of injection wells is evaluated for input of producers taking into account first time derivative from ratio of normalized oil production rate of flow-rate wells at operating production wells to normalized flow rate of injection wells at non-operating production wells of environment, and shifting of wells planned for injection is performed with due allowance for optimum duration of oil well injection, which corresponds to minimum value of first derivative.

EFFECT: technical result is higher efficiency of low-permeable formations.

1 cl, 3 dwg, 1 tbl

Description

The invention relates to the oil industry and can be used to increase the economic efficiency of the development of low-permeability formations.

A known method of developing an oil reservoir with a low-permeability reservoir [RU 2379491 C2, IPC E21B 43/20, publ. 20.01.2010], according to which, first of all, injection wells are constructed for advanced water injection (within 1-3 months) after oil development (no more than 7 days).

The disadvantages of this method are as follows. The method is applicable for a specific development system: a single-row development system with horizontal production and injection wells. The variability of reservoir distribution entails excessive geological risks when drilling ahead of injection wells: a weak or absent hydrodynamic connection between production and injection wells makes advanced water injection ineffective. It is not supposed to take into account the influence of the local geological environment of each individual development element, which directly characterizes the effectiveness of the reservoir pressure maintenance system (RPM).

The closest to the claimed technical solution is a method for determining the optimal development period of injection wells for oil using multivariate calculations on three-dimensional hydrodynamic models with direct alternate enumeration of various combinations of periods of development of injection wells for oil. One of the latest works, which mentioned the use of such a method - "Increasing the efficiency of areal waterflooding systems for low-permeability formations in Western Siberia", author Shupik N.V., dissertation for the degree of candidate of technical sciences, 2017.

Direct enumeration of options is ineffective in conditions of constant operational changes when drilling the planned well stock, however, it served as a reference for assessing the effectiveness of the method proposed in this work.

The technical problem to be solved by the present invention is the minimization of oil production losses when transferring injection wells for injection when developing low-permeability reservoirs with a pressure maintenance system.

The technical solution to this problem is to maximize early oil production in low-permeability reservoirs by timely transferring injection wells for injection.

The technical result of the invention consists in evaluating the optimal oil production period individually for each injection well.

The specified technical result is achieved by assessing the change in the intensity of the reaction of the injection well from the introduction of wells in the environment. The assessment is performed for each injection well for each time step of the period under consideration by calculating the first time derivative from the ratio of the normalized oil production rate of injection wells with active production wells in the environment to the normalized oil production of injection wells with non-operating production wells in the environment. The optimal life of an injection well for oil corresponds to the minimum value of the derivative described above. The advantages of the method are:

It does not contradict and is combined with accompanying physical processes that are taken into account when calculating flow rates, such as the effect of dissolved gas, change in permeability from saturation, and others.

Increased productivity compared to traditional methods due to fewer calculation iterations.

The field of application of the method does not depend on the selected development system with the maintenance of reservoir pressure. The proposed technical solution is illustrated by the figures.

FIG. 1 shows a diagram of the method.

FIG. 2 shows an example of the relative position of injection and production wells.

FIG. 3 shows an example of evaluating the optimal production period for injection well 19.

The essence of the approach is to determine the optimal oil production period individually for each injection well. The method of determination assumes the dependence of the injection efficiency of a particular well under consideration on interference, which is determined by assessing the change in the flow rate of an injection well, which is being developed for oil, from the introduction of the surrounding wells into production.

The method is carried out as follows.

Work is carried out in stages according to the diagram shown in FIG. one.

1. Selection of development elements (waterflooding).

An arbitrary number of development elements is selected, for which it is planned to transfer injection wells for injection. An example of the relationship between injection and production wells is shown in Fig. 2: 1-3, 5, 7, 10, 12-13, 16, 18, 20-21, 23, 25 - production wells, 4, 6, 8-9, 11, 14-15, 17, 19, 22 , 24, 26-27 - injection wells. These waterflooding elements, in whole or in part, can consist of both already drilled and planned wells.

2. Calculation of scenarios.

Predictive calculations of two scenarios are performed:

A. All wells (production and injection wells for design purposes) are put into production without transferring injection wells for injection;

B. Injection wells (Fig. 2: 4, 6, 8-9, 11, 14-15, 17, 19, 22, 24, 26-27) are put into production without conversion to injection, producing wells (Fig. 2: 1-3, 5, 7, 10, 12-13, 16, 18, 20-21, 23, 25) remain inactive.

The period of the forecast period is chosen arbitrarily at the discretion of the user. However, if the forecast period is too short, the user may not achieve the necessary difference in calculations for further evaluation.

3. Assessment of the response of injection wells to the commissioning of producers.

For each injection well, the normalized oil production rate is calculated in scenarios A and B for each time step of the forecast period.

- нормированный дебит нефти нагнетательной скважины в сценарии А на k-ом временном шаге, д. ед.;Where

- normalized oil production rate of the injection well in scenario A at the k-th time step, units;

q _{A k} is the oil production rate of the injection well in scenario A at the kth time step, t / day;

q _{A 0} is the initial oil production rate of the injection well in scenario A, t / day;

- нормированный дебит нефти нагнетательной скважины в сценарии Б на k-ом временном шаге, д. ед.;Where

- normalized oil production rate of the injection well in scenario B at the k-th time step, units;

q _{B k} - oil flow rate of the injection well in scenario B at the k-th time step, t / day;

q _{B 0} - the initial oil production rate of the injection well in scenario B, t / day;

Next, the ratio of the normalized oil production rate of the injection well in scenario A to the normalized oil production rate of the injection well in scenario B is estimated:

Then, the response of the operation of injection wells to the introduction of producers is evaluated using the first time derivative of the ratio i:

4. Estimation of the optimal life of the injection well.

The optimal period of injection well development is determined, corresponding to the minimum value of i '. FIG. 3 shows an example of an estimation of the optimal period of injection well development: 1 - normalized oil production rate of an injection well in scenario A; 2 - normalized oil production rate of the injection well in scenario B; 3 - ratio of the normalized oil production rate of the injection well in scenario A to the normalized oil production rate of the injection well in scenario B; 4 - the first time derivative of the ratio of the normalized oil production rate of the injection well in scenario A to the normalized oil production rate of the injection well in scenario B; 5 - the minimum value of the first derivative in time from the ratio of the normalized oil production rate of the reacting well in scenario A to the normalized oil production rate of the reacting well in scenario B.

The analysis of the inventive step showed the following: from the sources of patent documentation and scientific and technical literature, no technical solutions have been identified, which are based on features that coincide with the features of the proposed technical solution that ensure the achieved technical result.

An example of the implementation of the proposed method and performance evaluation.

An example of the analyzed area is shown in Fig. 2: 1-3, 5, 7, 10, 12-13, 16, 18, 20-21, 23, 25 - production wells, 4, 6, 8-9, 11, 14-15, 17, 19, 22 , 24, 26-27 - injection wells.

On the analyzed area (Fig. 2), the following calculation scenarios were performed using 3D hydrodynamic modeling:

Scenario A. All wells (production and injection wells as intended) are put into production in accordance with the planned commissioning date without transferring injection wells to injection.

Scenario B. Injection wells (Fig. 2: 4, 6, 8-9, 11, 14-15, 17, 19, 22, 24, 26-27) are put into production in accordance with the planned commissioning date without conversion to injection, producing wells (Fig. 2: 1-3, 5, 7, 10, 12-13, 16, 18, 20-21, 23, 25) remain inactive.

The forecast calculation period was 20 years with a step of 1 month in both scenarios.

In scenarios A and B, for each injection well, the normalized oil production rate was calculated according to formulas 1 and 2. Then, for each injection well, the ratio of normalized oil production rates i was calculated using formula 3 and the first time derivative of the ratio of normalized production rates according to formula 4.

For example, for well 19:

- initial oil production rate in the scenario A q _{A 0} = 15.25207, t / day;

- initial oil production rate in scenario B q _{B 0} = 15.25207, t / day;

- oil production rate at the 26th time step in the scenario А q _{A 26} = 7.6 1,023, t / day;

- oil production rate at the 26th time step in scenario B q _{B 26} = 11.07991, t / day;

- normalized oil production rate at the 26th time step in scenario A according to

formula (1):

- normalized oil production rate at the 26th time step in scenario B by

formula (2):

- the ratio of the normalized oil flow rates at the 26th time step in

formula (3):

- the first time derivative of the ratio of normalized flow rates at the 26th time step by the formula (4): i _'26 = d (i ₂₆₎ / dt = (i ₂₆ -i ₂₅₎ / (t ₂₆ -t ₂₅₎ = ( 0.68685-0.71733) / (26-25) = - 0.03048.

The table below shows oil flow rates, normalized oil flow rates in scenarios A and B, the ratio of normalized oil flow rates and the first time derivative of the ratio of normalized flow rates of well 19 at all time steps of the calculation.

FIG. 3 shows an example of evaluating the optimal period of the injection well 19: 1 - normalized oil production of the injection well in scenario A; 2 - normalized oil production rate of the injection well in scenario B; 3 - the ratio of the normalized oil production rate of the injection well in scenario A to the normalized oil production rate of the injection well in scenario B; 4 - the first time derivative of the ratio of the normalized oil production rate of the injection well in scenario A to the normalized oil production rate of the injection well in scenario B; 5 - the minimum value of the first derivative in time from the ratio of the normalized oil production rate of the reacting well in scenario A to the normalized oil production rate of the reacting well in scenario B. For injection well 19, the minimum value of the first derivative in time from the ratio of normalized production rates is reached at 26 time steps, therefore, for injection well 19, the optimal oil production period will be 26 time steps (in this example, the time step is a month).

Similar calculations of normalized oil flow rates, the ratio of normalized oil flow rates and the first derivative of the ratio of normalized oil flow rates were performed for the remaining injection wells. For each injection well, its own optimal production period was estimated (from 2 to 26 months). The increase in cumulative oil production over 20 years using the proposed method relative to the scenario with a fixed period of development of injection wells for oil was 2%.

Claims (1)

A method for determining the optimal oil recovery period for injection wells for low-permeability reservoirs, which consists in the fact that waterflooding elements are selected, representing drilled or design injection and production wells, for which it is planned to transfer injection wells for injection, and the injection wells are responsive and the dynamics are monitored flow rates, and the remaining wells are disturbing, perform predictive calculations for two scenarios when all wells: reacting and disturbing are put into production, and when the reacting wells are put into production, and disturbing wells are left idle, while determining the response of the injection well to the input of the producing , for which, for each injection well, the normalized oil production rate is calculated in each scenario for each time step of the forecast period, an assessment of the response of the operation of injection wells to the commissioning of production wells is performed, taking into account the first time derivative from the ratio of the normalized oil production rate of injection wells with operating production wells of the environment to the normalized production rate of injection wells with non-operating production wells of the environment, and the transfer of injection wells for injection is carried out taking into account the optimal production time of the injection well for oil, which corresponds to the minimum value of the first derivative.

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